Technical Field
The present disclosure relates to a programmable logic controller (PLC) system, and more specifically to central processing units (CPUs) of a PLC system.
Description of the Related Art
The demand for electric power increases with industrial development, and power use greatly differs between day and night, between seasons and between weekdays and holidays, the load factor becomes lower seriously.
Recently, to address such an issue, a variety of load management technologies for reducing peak load by utilizing excessive power is being developed. The battery energy storage system is one of the technologies.
The battery energy storage system stores excessive power at night or power generated from wind power, solar power, etc., and supplies the stored power to a load when the load reaches the peak or when an accident takes place in the system.
In this manner, it is possible to reduce the peak load and level the load.
Recently, smart grids attract attention as a variety of new and renewable energy sources are developed. Smart grids may also employ the battery power storage system.
Such a battery power storage system employs a control system using a PLC. The control system becomes more sophisticated and faster day by day and requires many additional functions in conjunction with IT technology.
In order to perform precise control, the operation of the PLC has to be predictable. However, as a number of IT technologies are combined, the CPU of the PLC has large load, which makes the operation of the PLC unpredictable.
To relieve such load, the CPU of the PLC is divided into a main CPU responsible for control function and a sub-CPU responsible for other function, such that the control operation of the PLC can be performed more easily.
Unfortunately, to operate such dual-CPU including the main CPU and the sub-CPU, an expensive dual-port RAM is required for sharing data between the main CPU and the sub-CPU. In addition, there is a problem in that delay time takes for sharing data between the two CPUs.